1. Field of the Invention
Aspects of the present invention relate to a burner for heating a fuel reformer that generates hydrogen, and more particularly, to a fuel reformer burner that can burn both a fuel gas and a hydrogen gas and that has increased combustion efficiency.
2. Description of the Related Art
A fuel cell is an electricity generation system that transforms chemical energy directly into electrical energy through a chemical reaction between oxygen and hydrogen, the hydrogen generally being contained in a hydrocarbon group material, such as methanol, ethanol, or natural gas.
A polymer electrolyte membrane fuel cell (PEMFC) system is a highly efficient next generation distribution type system that generates electricity and heat using an electrochemical reaction between hydrogen and air. The PEMFC fuel processor system includes a fuel cell stack and a fuel processor as main components and includes a fuel tank and a fuel pump as auxiliary components. The fuel cell stack has a structure in which a few to a few tens of unit cells, each formed of a membrane electrode assembly (MEA) and separators, are stacked. The fuel processor includes a fuel reformer and a shift reactor.
Hydrogen produced from the fuel processor is supplied to an anode electrode of the fuel cell stack and generates electricity and heat in the fuel cell stack through an electrochemical reaction with oxygen, which is supplied to a cathode electrode.
A reforming reaction in the fuel reformer and a shift reaction in the shift reactor are performed at high temperatures. Thus, the fuel processor includes a burner that provides heat required for the above reactions.
The fuel reformer burner generates heat by burning a fuel gas, and at this point, the fuel gas can be mainly hydrocarbon gas, such as, a city gas including mainly methane gas. However, in order to increase the efficiency of the PEMFC system, the burner must be able to burn not only the hydrocarbon fuel gas but also hydrogen gas. In other words, it is essential to include a device and method for burning unreacted hydrogen gas included in an anode-off gas (AOG) exhausted from the PEMFC system because the usage of the hydrogen gas in the fuel cell stack is generally 70 to 85% and thus, unreacted hydrogen gas is exhausted out of the fuel cell stack. Accordingly, the efficiency of the overall generation system can be increased by recovering the wasted hydrogen gas and using it as a fuel for the burner of the fuel processor.
Also, until a normal operation is achieved after starting up the fuel processor, hydrogen gas generated from the fuel processor is not supplied to the fuel cell stack for a few tens of minutes since the hydrogen includes a large amount of carbon monoxide (CO). Such large amount of CO can poison an MEA catalyst in the unit cell. The wasted hydrogen gas that includes a large amount of CO can be used as a fuel gas for the burner. In this way, the consumption of energy required for starting up the PEMFC system can be reduced.
In order to increase efficiency of the PEMFC system, a burner that can produce heat required for the fuel processor by using not only the hydrocarbon gas but also hydrogen gas included in the AOG as a fuel gas is beneficial. For this purpose, there is need for a burner that can efficiently and safely burn both types of fuels (a fuel gas and hydrogen gas).
In a conventional burner for a fuel reformer, air and AOG are mixed at a fuel inlet of the burner. However, hydrogen gas has a much faster burning rate than that of a fuel gas (e.g., ten times faster than methane). Thus, when burning the fuel gas, there is a high possibility that flames can proceed in a reverse direction of the fuel gas causing a back fire.